Production of low cold-test oils



Dec. 2, 1958 J. s. BROWN ETAL PRODUCTION OF LOW-COLD-TEST OILS Filed Deo. 1o. 1854 Egg;

Ja/m S. Brown Andrew 7T ./ancasek I N V EN TORS A ofiwfr United States Patent O PRODUCTION OF LOW COLD-TEST OILS John S. Brown, Flossmoor, Ill., and Andrew T. Jancosek, Hammond, Ind., assgnors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application December 10, 1954, Serial No. 474,549

4 Claims. (Cl. 208-25) This invention relates to the dewaxing of oils. More particularly, it relates to the preparation of low cold-test oils from wax-containing petroleum stocks.

The presence of waxes in hydrocarbon oils, even in small proportions, is commonly snicient to produce a significant increase in the pour point thereof, as cornpared with a wax-free oil of the same viscosity. It is conventional practice to remove a large proportion of the waxes from lubricating-oil stocks by selective precipitation of waxy materials at low temperature in the presence of a wax antisolvent, such as liquid propane, methyl ethyl ketone, or the like. All of these solvents, however, give oils of roughly the same pour point at comparable yields, and none of them is capable of producing a stock of suicently low pour point for a number of specialized uses, such as transformer oils, hydraulic oils, and refrigerator oils, without incurring excessive operating costs and undesirably poor yields. For these purposes, it has been common practice to choose a charging stock derived from low-wax crudes, such as Winkler or Kittrell. Oils in the SAE 5 to 10 range can readily be obtained therefrom in a simple manner.

Owing to the decreasing supplyof low-wax crudes,l

however, it has become necessary to devise another technique for producing low lcold-test oils, i. e., oils having pour points below about 0 F. A suggested method is urea-dewaxing, in which a wax-containing stock is treated with urea, and the urea reacts -with the straight-chain waxes and other normal paraiins of the oil, forming compounds with the straight-chain hydrocarbons called adducts, which are insoluble in the oil and are readily removed therefrom by filtration. 'Because the high pour point of an' oil is usually due to the presence of straight chain paraiiin waxes, removal vof these waxes produces an oil of low pour point. Unfortunately,v however, oils in the usual viscosity range of low cold-test oils (i. e., around 40 to 300 SSU at 100 F.) do not form urea adducts to any considerable extent under the conditions employed in the prior art. It is accordingly an object of our invention to provide a method of urea-dewaxing applicable to the treatment of wax-containing stocks in the viscosity range of low cold-test oils. Another object is to prepare oils yof low pour point in improved yields. A further object is to improve the -pour point of solvent-dewaxed oils. Still another object is to improve the effectiveness of adduct formation between urea and waxes. Another object is to improve the urea dewaxing of hydrocarbon oils in a cyclic process. These and other objects of our invention will be apparent from the following description and the `appended claims. y

We have developed a technique and conditions, ernployin'g urea-dewaxing in the presence of a critical proportion of methanol and water, whereby wax-containing l oils in the low cold-test range (e. g., having a viscosity up to about 300 SSU at 100 F.) can readily be treated and reduced in pour point to the range of about to 70 F. In our new process, a wax-containing stock, preferably-after a preliminary solvent-dewaxing step, is

Patented Dec. 2, 1958 r, ICC

subjected to contact with area under adduct-forming conditions in the presence of about 0.05 to 0.5 mole of methanol per mole of urea and about 2 to 10 volume-percent of water based on the methan'ol. The urea and wax form an insoluble adduct, which is readily. filtered from the oil, leaving a treated oil having a pour point within the desired range. The urea is conveniently recovered by known methods and can be cyclically reused.

We have demonstrated that wax-containing hydrocarbon oils ranging in viscosity from around 40 to 300 SSU at F. and in pour point from about 0 to 100 F. are reduced in pour point byurea dewaxing according to our new technique. These viscosities correspond in general to the SAE 10, SAE 5, and lighter grades. The prior-art urea-dewaxing techniques are largely ineffective in this range. Our process can be used, for example, to treat a mineral seal oil of 45 SSU viscosity at 100 F. and pour point around 35 F., yielding a treated oil having a pour point of 70 F., which is more than' adequate for most uses. The minimum pour point attainable appears to depend on the viscosity of the oil, varying directly as a logarithmic function thereof. Previous solvent dewaxing, in some cases, also affects the pour point obtained by urea dewaxing according to our technique. Oils having viscosities of 40 to 150 SSU at 100 F. ureadewax to the same low pour point whether previously dewaxed or not. In the viscosity range of -200 SSU, urea dewaxing produces oils of low pour point only from oils which have been .previously dewaxed by other means-e. g., by propane dewaxing, cold pressing, or the like. From 200 to 300 SSU, urea forms adducts with the waxes in 'both distillates (undewaxed) and cold-pressed oils, but the improvements in pour point are n'ot as great. Urea dewaxing also tends to increase the viscosity of the treated oil, ordinarily up to about l0 percent. f Our process represents a marked improvement over the prior art, which has devoted considerable study to the problem of removing waxes from wax-containing petroleum oils by treatment with urea. A variety of conditions have heretofore been' tried in an effort to establish the operative as well as the preferred conditions for the process. None of the art, however, has employed or suggested the critical proportions of methanol and water ernployed as an activator in our process, and in fact the art, as exemplified by British Patent 671,456, indicates that the advantageous results of our process would not be obtained under the condition's employed therein.

VIn a simple embodiment of our invention, a wax-containing charging stock is commingled with urea and a critical proportion of methanol and water, option'ally in the presence of a diluent'hydrocarbon liquid, and the mixture is agitated at ordinary temperature, whereupon an insoluble wax-urea adduct is formed. The slurry is filtered by conventional means, suitably through an ordinary canvas filter, air pressure being used as needed to speed the filtration. The diluent liquid serves to reduce the viscosity of the reactants and to minimize retention of charging stock on the adduct. If no diluent is used, around 10 percent of the dewaxed oil is ordinarily retained on the adduct, an'd can be removed by washing with, for example, half a volume of a light naphtha, based on the charging stock. The Vfiltrate and washings are combined and stripped of diluent to give the desiredy low cold-test product. Any dissolved methanol is simultaneously removed, and can be recovered from the stripper overhead. The wax-urea adduct is slurried with additional diluent liquid an'd heated above 160 F., preferably between about 175 yand 250 F. This treatment decomposes the adduct and liberates the urea, wax, methanol,V and water. The methanol is driven off as avapon'. which is condensed and recovered forrecycle. 1 TheV wax,

dissolves in the diluent liquid, and the urea forms a slurry therein. The urea is separated by filtration, centrifugation, or the like, and is thereby recovered in a form suitable fo`r' reuse in the treatment of additional charging stock; The wax is recoverable from the diluent liquid solution by stripping.

The attached drawiiig illustrates a batch-type embodiment of our invention, in which a prop'ane-'dewaxed Mid- Continent SAE 5 distillate is diluted with a heavy' alkylate fraction and urea-treated in vthe presence of our critical proportions of methanol and water, the ewaxed oil is withdrawn from the resulting urea-wax adduct and any unreacfed urea, the adduct is decomposed by heating with heavy alkylate, which dissolves the' liberated wax, the solution of wax in' alkylate is filtered from the regenerated urea, and th'ealkyflateis distilled' from the wax.

In the drawing, the charging stock, supplied through line 1I`,- together with'our activatingproportion of methanol and water, supplied through line 12, and heavy alkylate, supplied through valved line 13, is introduced by pump 14 into reaction vessel 15, containing solid, finely divided urea. Within the reactor, the charged materials and urea are intimately commingled by agitator 16 until urea-wax adduct formation has reached substantial completion. Thereafter, an inert gas is' introduced through line 17 into the top of the reactor, and pressure is applied thereby, forcing the dewaxed oil phase through filter medium 18 (suitably canvas supported on a screen) and out through valved line 19 into storage vessel 20.

From storage vessel 20, the dewaxed oil is conveyed by pump 21 through heater 22 into stripper column 23 at an intermediate point. Therein, the oil is strippedl of alkylate to the desired flash point with steam, introduced into a lower section of the column through line' 24. A vaporous distillate emerges overhead through cooler 25 into decanter 26, where a water phase separates and is withdrawn' through line 27. The organic phase, consisting principally of recovered alkylate, is reuxed in part to the top of the column'thro'ugh valved line 28', and is withdrawn in part through valved line 29 to storage vessel 30' for recycle.- Make-up alkylate is supplied as required through line 31. From the bottom of column 23, the desired oil of low pour point emerges through cooler 32. It can be further treated if desired to remove any entrained water or other haze-forming substancesl accord; ing to methods known in the art (equipment not shown),

Remaining' within reactor 15 is a filter cake, consisting essentially of urea-wax adducts, methanol, water, and unreacted urea. The a'dducts are decomposed. by introducing heavy alkylate by' way of pump 33, valved line 34, pump 35, heater 36', and line 37 into an upper section of reactor 15. The resulting,l slurry is re'circ'u'lat'ed by way of line 38; pump 35, heater 36, and lin'e 37 to permit the stream to be heated to a temperature above the decomposition point of the adduct butl below the melting point of urea"i.V e., above about 160 F. and below 270 F., preferably between about 175 and 250 F. Overheating tends to decompose the urea, but not to a significant extent b'elow about 275 F. During'l the heating cycle, methanol is driven ofir overhead through valved line 39, and is condensed by cooler 40 and led through line 41 into storage tank 42. Make-up methanol and water are supplied to the said tankV respectively through lines 43 and 44.

After the decomposition of the adduct is substantially complete, pumpv 36 is shut off, and the urea slurry is again filtered by introducing inert gas under pressure through line 17. The waX-alkylate solution is withdrawn through valved line 45 to equipment (not illustrated) for' separately recoveringthe wax and heavy alkylat'e.

Reaction vessel 15 is left with a filter cake of finely divided, solid, crystalline urea, suitable for immediate reuse in treatin'ganother batch of charging stock accord'- in'g to the procedure outlined above'. Make-up urea is supplied as needed. Y y t An important feature of our invention lies in the use of a new activator composition to effect successful formation of urea-wax adducts. Only the concurrent use of methanol and water in a volume ratio between about :10 and 98:2 has been found to be satisfactory as an adduction activator for lowering the pour point of oils of SAE 10 grade and lower. Other proportions of methanol and wafer and other types of activators produce substantially no pour-point lowering with these stocks. We ordinarily employ our activator in the proportion of about 0.5 to 4 gallons per hundred pounds of urea, and we prefer to employ aqueous 94 to 97 percent methanol in the proportion of around 1 to 2 gallons per pounds of urea.n

The formation of an adduct between urea and waxy normal parafns proceeds at any temperature below about F, Ordinary temperatures in the range of about 75 to 80 F. are preferred. Temperatures above 100 F. are less satisfactory, because the activator tends tov be driven off, and temperatures below about 50 F. are less satisfactory because of contacting and filtering diiculties arising from increased viscosity of the reaction mixture.

The ratioV ofv urea to charging stock in our process varies considerably, depending upon the wax content thereof. Ordinarily, at least about 3 pounds, and preferably about 4 pounds or more, of urea are required to effect complete removal of 1 pound of wax. For example, a propane-dcwaxed oil such as a Mid-Continent SAE 10 stock, which contains approximately 0.4 pound of adductible material per gallon, requires at least about 1.6 pounds of urea per gallon of oil for best results; A smaller urea'zwax ratio gives incomplete wax removal and less than the maximum pour-point lowering. We prefer to contact urea and charging stock in the proportion of around 4 to 8 pounds of free urea per pound of adductible wax contained in the stock.

In the treatment of high-viscosity oils and/or high-wax stocks, the nature of the adduct hinders agitation and filtering of the reaction slurry. In such cases, a diluent naphtha such as heavy alkylate is added to the charging stock to thin the mixture. This results in better contact between the urea and oil as well as more rapid filtering. The quantity of diluent to be used in any case will depend upon the viscosity of the charging stock, the wax content thereof, the mixing efficiency of the equipment, and the'desired filtration rate'. It is of course desirable to use diluents in as low a concentration as possible in order to minimize the difficulty and expense ofrecovery thereof. We have foundV that diluents can conveniently and advantageously be employed in proportions up to 200 percent or more based on the charging-stock oil, depending largely upon the viscosity thereof. When a diluent is indicated, we prefer to employ between about 50 and 100 percent thereof, based on the charging stock. Many hydrocarbon liquids are suitable for this purpose so long as they are wax-free, although it will be apparent that the results obtained therefrom are not necessarily equivalent. We have successfully employed naphthas and other hydrocarbons, including pentane, isopehtane, isooct'ane, benzene, toluene, light alkylate, heavy alkylate, and the like. Liquids of the same class are suitable for use in the adduct-'decomposition step'.

In an advantageous embodiment of our process einploying a diluent liquid, we use the same diluent in both adducting and regenerating the urea. For this purpose, it is desirable to choose a high-boiling naphtha which is inert to 'urea at all temperatures and which has a 1ow vapor pressure atthe temperatures employed in adduct decomposition. Our preferred diluent is a heavy alkylate, obtained' for example' asv a bottoms fraction from' the p'roduction of iso'octane by alkylation. This material is inert to urea at all temperatures (as contrasted with pentane, which forms an adduct at: 10 R), and has an initial boiling" point of 350'o F; A- desir'able alkylate fraction has a boiling range of about 350 to 800 F. Heavyalkylate` is a clean material which does not aect the reactivity of the urea and does not adversely affect the urea-treated oil. It s therefore unnecessary to wash this material out of the urea, or to strip it completely out of 5 the treated oil. It is only necessary to strip the oil to the desired flash point. Any alkylate remainingtherein is highly branched, and is benecial rather than detrimental to the treated oil. Another advantage. of heavy alkylate lies in its facilitation of methanol recovery. During the heat decomposition of the urea adducts in the presence of alkylate, the methanol is selectively driven olf as a vapor stream, which is readily condensed and recovered for recycle. Finally, when the adducts have been broken by heating with alkylate, it is unnecessary to strip the alkylate from the wax unless the wax is desired as a separate product. The wax-alkylate solution can be sent directly to catalytic cracking, if desired, where full value for the alkylate will be realized, and the wax will be cracked to desirable products.

Our invention will be more fully understood from the following specific examples.

Example 1 A mineral seal oil having a viscosity of 40 SSU at 100 F. and a pour point of 35 F. was dewaxed according to the following procedure. A 14-pound portion of the said oill was commingled with 17.9 pounds of heavy alkylate, 12 pounds of urea, and 740 milliliters of aqueous 97 percent methanol, and the mixture was agitated at ordinary temperature (around 75 F.) for 5 minutes until adduct formation had reached substantial completion. The resulting slurry was filtered. The iiltrate was stripped to a ash point of 214 F. (Pensky- Martens Closed Cup), yielding 11.3 pounds of dewaxed oil having a viscosity of 43.5 SSU at 100 F. and a stable pour point of 70 F.

Example 2 A 5W oil having a viscosity of 89 SSU at 100 F. and a pour point of F. was obtained by solvent extracting and propane dewaxing a suitable Mid-Continent stock. The said oil was dewaxed according to the procedure described in Example l, employing 15 pounds of the oil, 18.8 pounds of heavy alkylate, 12 pounds of urea, and 760 milliliters of aqueous 97 percent methanol, in the reactor charge. The treated product oil weighed 14.3 pounds and had a viscosity of 99.1 SSU at 100 F. and a pour point of 35 F. 4

Example 3 An SAE 5 Mid-Continent distillate having a pour point of 60 F. and a viscosity of 83.4 SSU at 100 F. was dewaxed according the the following procedure. The SAE 5 distillate (868 grams) was commingled with 2 liters of pentane, 1200 grams of urea, 175 milliliters of aqueous 99 percent methanol, and 2 milliliters of water and agitated at ordinary temperature for approximately 5 minutes. The resulting slurry was filtered, and the filtrate was stripped substantially free of pentane, methanol, and water, yielding 641 grams of a treated oil having a pour point of -35 F. and a viscosity of 100.3 SSU at 100 F.

Example 4 An SAE propane-dewaxed Mid-Continent distillate having a viscosity of 202 SSU at 100 F. and a pour point of 0 F. was dewaxed according to the following procedure. The charging stock (608 grams) was commingled with 2 liters of pentane, 200 grams of urea, and 35 milliliters of aqueous 97 percent methanol, and the mixture was agitated for approximately 5 minutes at ordinary temperature. The resulting slurry was filtered, and the filtrate was stripped substantially free of pentane, methanol, and water. Thedewaxed product oil had a pour point of 25 F. and a viscosity of 220.8 SSU at F., and weighed 5 82 grams, corresponding -to a yield of 95.5 percent.

Example 5 The following tests were carried out on the ureadewaxing of an SX l0 base oil having a viscosity of 165 SSU at 100 F. and a pour point of 0 F., obtained by solvent extracting and propane dewaxing a suitable Mid- Continent stock. Aqueous methanol was employed as the activator in each case. Little or no urea-adduct formation was observed with methanol containing water at the levels of 1 volume-percent and 13 volume-percent, whereas excellent adduct formation was obtained with methanol containing 8 percent of water. The tests were as follows:

A. A mixture of 1297 grams of the base oil, 455 grams of urea, 75 milliliters of aqueous 99 percent methanol, and 2 liters of pentane were reacted at room temperature. The resulting slurry was ltered, the iilter'cake was washed with around 1.5 to 2 liters of pentane, and the combined filtrate and washings were stripped to a iiash point of 435 F. The oil recovered thereby had a pour point of 0 F., identical with 'the charging stock.

B. A 1276-gram portion of the base oil was reacted according to the same procedure with 460 grams of urea, 65 milliliters of aqueous 99 percent methanol, l0 milliliters of Water, and 2 liters of pentane. The treated oil obtained thereby was found to have a viscosity of SSU at 100 F. and a pour point of 5 F., substantially the same as the charging stock.

C. A 1282-gram portion of the base oil was reacted according to the same procedure with 460 grams of urea, 65 milliliters of aqueous 99 percent methanol, 5 milliliters of Water, and 2 liters of pentane. The treated oil was found to have a pour point of -25 F., and a viscosity of 177 SSU at 100 F.

While we have described our invention with reference to certain specific charging stocks, operating conditions, and processing techniques, it is to be understood that such details are included only by way of illustration, and not by way of limitation. For example, it will be apparent that our process can be carried out in a continuous or semicontinuous manner, utilizing for this purpose reaction vessels and auxiliary equipment of the types described in and available to the art. Numerous modiications and equivalents of the invention will be apparent from the foregoing description to those skilled in the art.

as our invention:

1. A cyclic process for urea-dewaxing a wax-containing hydrocarbon oil having a viscosity between about 40 and 300 SSU at 100 F. and obtaining a low cold-test oil therefrom having a pour point in the range of about v 10 to 70 F., which comprises contacting the said oil under urea-adduct forming conditions with solid urea in the presence of a diluent hydrocarbon liquid and between about 0.05 and 0.5 mole of aqueous methanol per mole of urea, said aqueous methanol containing between about 2 and 10 percent by volume of water, separating urea adducts and any unreacted urea from the resulting slurry, stripping diluent liquid from the treated liquid resulting therefrom, whereby a treated oil of decreased pour point within the desired range is obtained, decomposing said urea adducts by contacting said adducts with a quantity of said diluent liquid at an elevated temperature above about 175 F. and below the melting point of urea, whereby methanol contained therein is liberated as a vapor stream and the waxes are liberated and dissolved in said hydrocarbon liquid, separating solid, nely divided urea from the resulting slurry, and recovering and reusing said methanol and said urea to contact additional charging stock.

2. A cyclic process for urea-dewaxing a wax-containing hydrocarbon oil having a viscosity between about 40 and 300 SSU at 100 F. and obtaining a low cold-test oil there..

In accordance with the foregoing description, we claim l 7 from having" a pour p'in't" the 'range offabo'ut -10 to -70 F., which comprises diluting said oil w'itla heavy alkylate boiling between ab'out350 and 800 F. and contacting the diluted oil; at ordinary temperatures with at Ieast about 4 pounds' of solid urea per pound of wa'X contained'in said oil'an'd between about 1 and 2 gallons of aqueous methanol per 100 pounds ofl urea",v said aqueous methanol containingbetween about 3 and 6percent by vol' ume of water, separating u'ea adducts and .any unreacted urea from the resulting slurry, stripping heavy alkylate from the treated liquid resultingl therefrom, whereby a treated oil of decreased pour point within' the desired range is obtained, decomposing said urea adducts by contacting said adducts with a quantity of heavy alkylatel aty an elevated'temperatu're between about 175 F. and 250 F., whereby the methanol contained therein is2liber'ated as a vapor stream and the waxes are' liberated and dissolved in` said heavy alkylate, separating solid, nely divided urea from the resulting slurry, and recovering and reusing said methanol and said urea to contact additional charging stock.

3. A method for dewairing a wax-containing' hydrocarbon oil having a viscosity between about 40 and 3'00 SSU at 100 F. and a pour point between about 0' and 100 F. and obtaining a low cold-test oil therefrom having a pour point in the range of about -10 to -70'F., which comprises contacting said oil with solid urea' under' urea-adduct forming conditions in the presence of between about 0.05 and 0.5 mole of methanol per mole of urea and between about 2 and 10 volume-percent of water based' on said methanol, whereby urea` adductsI areform'ed from the' waxes contained in sad' oil, and separatingsfaid urea adduct's and any unreacted urea fron'ilthe yrer'sflulting raction' mixture, whe'r'eby a low cold-test oil' of the de# sir'ed pour-point range is obtain'edl 4. A mailed fr treating a w'ayomaming Mdfcotin'ent oilV of not greater than SAE 10'viscos`ity and pour' point between'about 0 and 100 F. and obtaininga low o co1d= test` oil' therefrom having a pour point in the range o'f about 10 to '--70a F., which comprises contactingv said wax-'containing oil with` solid urea in the proportion` References- Citedv in the le of this patent UNrTED STATES PATENTS 2,661,317 Skelton e't al. Dec. 1, 1953 2,663,671 Wiles et al. Dec. 22, 1,953 2,672,457 Weedman Mar. 16 1954 2,681,335 Gorin V June 15, 1954 2,731,455 Salzmann et al. Jan.1l7, 1956 2,731,456 Weedman Ian. 17, 1956` 

3. A METHOD FOR DEWAXING A WAX-CONTAINING HYDROCARBON OIL HAVING A VISCOSITY BETWEEN ABOUT 40 AND 300 SSU AT 100*F. AND A POUR POINT BETWEEN ABOUT 0 AND 100*F. AND OBTAINING A LOW COLD-TEST OIL THEREFROM HAVING A POUR POINT IN THE RANGE OF ABOUT -10 TO-70*F., WHICH COMPRISES CONTACTING SAID OIL WITH SOLID UREA UNDER UREA-ADDUCT FORMING CONDITIONS IN THE PRESENCE OF BETWEEN ABOUT 0.05 AND 0.5 MOLE OF METHANOL PER MOLE OF UREA AND BETWEEN ABOUT 2 AND 10 VOLUME-PERCENT OF WATER 